The invention relates to a debris cap mechanism for use in connection with a housing to enclose and protect a re-entry hub of a subsea well.
The development of subsea oil and gas production equipment particularly for remote controlled operation is a relatively new field and presents new problems not encountered by land based and platform operations. Generally, the subsea equipment must be highly reliable, have a long service life, and have a low pollution hazard.
Generally, the debris cap for the protection of the subsea re-entry hub or wellhead should meet the following requirements. The debris cap should provide a protective cover over the re-entry hub and the housing circumferentially surrounding the well. The debris cap should be preferably flush with the top edge of the housing to prevent debris and other objects from damaging the hub or otherwise interfering with the subsea operations. In practice, the debris cap can be cleared of objects by the use of a water jet.
When the debris cap is in its closed position, there should be a leak type closure with respect to the housing. The debris cap and the housing defines an enclosure in which oil and gas rising from sources below it are accumulated and can be monitored in order to evaluate the pollution hazard.
It is of great importance that the debris cap be removable during the wellhead work over operations in order to join a re-entry connector on a handling tool to the re-entry hub. The removal of the debris cap should be simple and preferably passive. Preferably, actuators on the handling tool should be operable to move the debris cap aside.
Additionally, it is anticipated that there is a possibility that the production equipment might have leaking which will be trapped under the debris cap so that it is preferable to provide a vent for the gas.
In practice, it is expected that the debris cap will be used at depths to 1,000 feet and must be designed to resist corrosion due to sea water, crude oils, and hydrogen sulfide gas. A selection of metals must be made to avoid the formation of galvanic cells.